High amplitude tube-waves hamper seismic measurements in boreholes. By "tube-wave," we mean a Stonely wave that propagates along a borehole with a wavelength much greater than the diameter of the borehole. These tube-waves are created by the coupling of seismic waves in a liquid-filled borehole. They propagate within the borehole with very little attenuation.
In a seismic borehole survey many different seismic waves intersect the borehole, including the direct P and S waves, surface waves, and reflected P and S waves. Each of these waves generates tube-waves inside the borehole. In addition, tube-waves are reflected at the bottom of the well, at the top of the liquid column, at lithologic boundaries, and at changes in the borehole diameter. These tube-waves are generally recognized as high amplitude coherent wavetrains, but as the innumerable low amplitude tube-waves interfere with one another, they also create a background of incoherent seismic noise.
Because of these tube-waves, borehole seismic measurements are usually made with geophones, which can be tightly clamped to the borehole wall making them less sensitive to tube-wave motion. If it were not for the tube-waves, hydrophones would be preferred over geophones because a large number of hydrophones can be deployed at the same time, thereby shortening the time required to conduct the survey. Unfortunately, hydrophones are not clamped to the borehole wall and are thus much more sensitive to tube-wave noise than are geophones. In fact, this noise so dominates the record that hydrophones are seldom used in borehole seismic surveys.